CO2 laser collective Thomson scattering diagnostics on the HT-7 tokamak

A CW CO2 laser collective Thomson scattering diagnostics was developed to measure plasma density fluctuations on the HT-7 tokamak. The design and construction of CO2 laser scattering apparatus is described. The laser source is a continuous-wave CO2 laser with a cavity length of 1.9 m and a power output of about 10 W at 10.6 μm. The k-resolution of the system is △k ≈ 3.2 cm^-1. The preliminary data from the diagnostic is presented.     

Design and development of a synchronized operation control system for Thomson scattering diagnostic on J-TEXT

A Thomson scattering diagnostic system is under construction at the Joint Texas Experimental Tokamak (J-TEXT).A 1064 nm Nd:YAG laser with 50 Hz repetition rate is used as the laser source.We have used a software for careful and precise control of the laser through serial communication.A time sequence operating system has been developed to synchronize the laser control and data acquisition system with the central control system (CSS).The system operates commands from the CSS of J-TEXT and generates triggers for the laser and data acquisition system in the proper sequence.It also measures an asynchronous time value that is needed for accurate time stamping.All functions are served by a field-programmable gate array development platform that is suitable for high-speed data and signal processing applications.Several embedded peripherals,including Ethernet and USB 2.0,provide communication with the CSS and the server.     

HCN Laser Interferometer on the EAST Superconducting Tokamak

A single-channel far-infrared （FIR） laser interferometer was developed to measure the line averaged electron density on the EAST tokamak. The structure of the single-channel FIR laser interferometer is described in detail. The evolution of density sawtooth oscillation was measured by means the FIR laser interferometer, and was identified by electron cyclotron emission （ECE） signals and soft X-ray intensity. The discharges with and without sawtooth were compared with each other in the Hugill diagram.     

Development of an HCN dual laser for the interferometer on EAST

A two-color continuous wave(CW) discharge-pumped far-infrared(FIR) hydrogen cyanide(HCN) laser was developed as the source of an interferometer for measuring the line-averaged electron density in the Experimental Advanced Superconducting Tokamak(EAST). The output power of the dual laser system was about 120 m W from each laser on the 337 μm(0.89 THz)line. The polarization of each output beam was fixed using thin tungsten filaments and oscillated in the EH11 mode. Different megahertz intermediate frequencies(IF) and a slight frequency offset(～1 MHz) were generated in this system to replace the traditional rotating grating with～10 k Hz IF, and this can improve the time resolution of the interferometer significantly. The experimental result showed that different IF signals were obtained by successfully adjusting the cavity length. In particular, the beat frequency was captured at ～1.3 MHz by a Schottky mixer when the length of the resonant cavities was changed by 5 μm by an automatic adjustment system. In order to study the character of IF, a long time record of the IF signal was carried out,and the IF signal could be stabilized for a few minutes in the range of 2 MHz to 3 MHz. A realtime IF stability control system was initially designed for long pulse discharge experiments on the EAST. The ～MHz frequency response and good phase sensitivity of the dual laser HCN interferometer will allow the system to track fast density profiles and resolve fast MHD events,such as tearing/neoclassical tearing, disruptions, etc.     

Development of the pellet injection system on the J-TEXT tokamak

Pellet injection is an attractive technology for core-fueling and magnetohydrodynamic study in magnetic-confinement fusion devices like tokamaks and stellarators. It can inject solid hydrogen/deuterium pellets into the plasma with deeper density deposition compared with other fueling methods, such as gas puffing. A three-barrel H₂ pellet injection system was installed on the J-TEXT tokamak and experiments were carried out. The pellets are formed in three barrels cooled by a cryocooler and compressor system at around 9 K, and are 0.8 mm/1 mm diameter and 0.8 mm length. The pellet is launched by helium propellant gas and injected from the low-field side of the plasma. The normal range of pellet speed is 210–310 m s⁻¹ for different propellant gas pressures. Due to the three-barrel structure, the number of injected pellets can be adjusted between one and three. Pellets can be launched sequentially with arbitrary time intervals, which enables flexible applications. The results of the experiments show that pellet fueling efficiency can reach 50%. The energy confinement time increased by about 7.5‒10 ms after pellet injection.     

The application of limiter target electrostatic measurement system in J-TEXT tokamak

The limiter target electrostatic measurement system including limiter grounding current sensors and Langmuir probes have been newly developed for the measurement of the limiter target area on the Joint-Texas Experimental tokamak(J-TEXT).Current sensors fixed between graphite limiters and the vacuum vessel walls are used to measure the currents between limiters and vessel wall.Simultaneously,a rectangular poloidal array containing 54 Langmuir probes is embedded in the graphite tiles of limiters for a more localized measurement.Based on this system,the effect of both the plasma's inherent behavior,including plasma motion and the 2/1 tearing mode,and the electrode biasing on probe and sensor signals have been observed and analyzed in the experiments.     

Recent progress on the J-TEXT three-wave polarimeter-interferometer

The J-TEXT three-wave polarimeter-interferometer system (POLARIS), which measures time-space distribution of electron density and current density, has been optimized with both the optical system and the equilibrium reconstruction method. The phase resolution of a Faraday rotation angle has been improved from 0.1 to 0.06 degree in chords from –0.18 to 0.18 m (plasma minor radius), and the sawtooth oscillation behavior has been detected by Faraday rotation angle measurement. By combining the POLARIS measured data and the equilibrium and fitting code (EFIT), an upgraded equilibrium reconstruction method has been developed, which provides a more accurate temporal and spatial distribution of current density and electron density. By means of the optimized POLARIS and improved equilibrium reconstruction, variations of profiles with increasing density have been carried out, under both Ohmic and electron cyclotron resonance heating discharges.     

The timing system on the J-TEXT tokamak

This paper describes the timing system designed to control the operation time-sequence and to generate clocks for various sub-systems on J-TEXT tokamak. The J-TEXT timing system is organized as a distributed system which is connected by a tree-structured optical fiber network. It can generate delayed triggers and gate signals (0 μs–4000 s), while providing reference clocks for other sub-systems. Besides, it provides event handling and timestamping functions. It is integrated into the J-TEXT Control, Data Access and Communication (J-TEXT CODAC) system, and it can be monitored and configured by Experimental Physics and Industrial Control System (EPICS). The configuration of this system including tree-structured network is managed in XML files by dedicated management software. This system has already been deployed on J-TEXT tokamak and it is serving J-TEXT in daily experiments.     

Pulse-burst laser-based 10kHz Thomson scattering measurements

Thomson scattering(TS),as a popular and reliable diagnostic technique,has successfully measured electron temperatures and electron number densities of plasmas for many years.However,conventional TS techniques using Nd:YAG lasers operate only at tens of hertz.Here,we present the development of a high-repetition-rate TS instrument based on a high-speed,pulse-burst laser system to greatly increase the temporal resolution of measurements.Successful instrument prototype testing was carried out by collecting TS light from laboratory helium and argon plasmas at 10 kHz.Calibration of the instrument detection sensitivity using nitrogen/oxygen rotational Raman scattering signal is also presented.Quantitative electron number densities and electron temperatures of the plasma were acquired at 10 kHz,for stable plasma discharges as,respectively,～0.9 eV and ～5.37×10~(21)m~(-3) for the argon plasma,and ～1eV and ～6.5×1021 m~(-3) for the helium plasma.     

Characterization of heat transport dynamics in laser-produced plasmas using collective Thomson scattering: Simulation and proposed experiment

We propose an experiment in which the collective Thomson scattering lineshape obtained from ion acoustic waves is used to infer the spatial structure of local heat transport parameters and collisionality in a laser-produced plasma. The peak-height asymmetry in the ion acoustic wave spectrum will be used in conjunction with a recently developed model describing the effects of collisional and Landau damping contributions on the low-frequency electron density fluctuation spectrum to extract the relative electron drift velocity. This drift arises from temperature gradients in the plasma. The local heat flux, which is proportional to the drift, can then be estimated, and the electron thermal conductivity will be inferred from the relationship between the calculated heat flux and the experimentally determined temperature gradient. Damping of the entropy wave component at zero mode frequency is shown to be an estimate of the ion thermal conductivity, and its visibility is a direct measure of the ion-ion mean free path. We also propose to measure thermal transport parameters under dynamic conditions in which the plasma is heated impulsively by a laser beam on a fast (50 ps) time scale. This technique will enable us to study heat transport in the presence of the large temperature gradients that are generated by this local heating mechanism. Deviations of the inferred local thermal conductivity from its Spitzer-Härm value can be used to study the transition to a nonlocal heat transport regime. We have constructed a simple numerical model of this proposed experiment and present the results of a simulation.This work was performed under the auspices of the U.S. Department of Energy by Sandia National Laboratories under Contract DE-AC04-94AL85000 and by Lawrence Livermore National Laboratory under Contract W-7405-ENG-48.     

Design of Thomson scattering diagnostic system on linear magnetized plasma device

In addition to the magnetic confinement fusion plasma, Thomson scattering has been applied to measure electron density and temperature of low-temperature plasmas. Based on a linear magnetized plasma device, a set of Thomson scattering diagnostic system is designed to diagnose the plasma with ${n}_{{\rm{e}}}={10}^{18}{\unicode{x02013}}{10}^{19}\,{{\rm{m}}}^{-3}$ and ${T}_{{\rm{e}}}=2{\unicode{x02013}}5$ eV. Due to low plasma temperature and density, this diagnostic system needs high spectral resolution and collection efficiency to meet the requirements of electron velocity distribution function measurements. Through the bench test, it is confirmed that the spectral resolution reaches 0.01 nm, and theoretical collection efficiency is high enough to obtain a Thomson scattering spectrum by 1000 accumulations.     

The Construction of Plasma Density Feedback Control System on J-TEXT Tokamak

The plasma density feedback control system(PDFCS) has been established on the Joint Texas Experimental Tokamak(J-TEXT) for meeting the need for an accurate plasma density in physical experiments.It consists of a density measurement subsystem,a feedback control subsystem and a gas puffing subsystem.According to the characteristic of the gas puffing system,a voltage amplitude control mode has been applied in the feedback control strategy,which is accomplished by the proportion,integral and differential(PID) controller.In this system,the quantity calibration of gas injection,adjusted responding to the change of the density signal,has been carried out.Some experimental results are shown and discussed.     

高功率HCN波导激光器研制

主要叙述为HL-2A装置多道远红外(FIR)激光干涉仪而设计研制的一台高功率cw HCN分子波导激光器。按照337μm波导激光器定标定律选算出输出功率大于400 mW的HCN激光器几何结构参数(放电长度5.6 m,波导放电管内直径φ6.3 cm)。讨论了获得连续稳定输出的运行参数范围和大体结构。对激光器整体做了综合考虑,诸如热阴极采用了发射电流密度大的LaB_6材料,用殷钢棒稳固谐振腔长的光桥结构以及精确腔准直平移的全反射镜端机械调节结构,送排气管道的半定量估算等。给出激光器运行参数的初步调试实验结果。     

The anode power supply for the ECRH system on the J-TEXT tokamak

The electron cyclotron resonance heating(ECRH) system with a 60 GHz/200 k W/0.5 s gyrotron donated by the Culham Science Center is being developed on the J-TEXT tokamak for plasma heating, current drive and MHD studies. Simultaneously, an anode power supply(APS) has been rebuilt and tested for the output power control of the gyrotron, of which the input voltage is derived from an 80 k V negative cathode power supply. The control strategy by controlling the grid voltage of the tetrode TH5186 is applied to obtain an accurate anode climbing voltage, of which the output voltage can be obtained from 0-30 k V with respect to the cathode power supply. The characteristics of the APS, including control, protection, modulation, and output waveform, were tested with a100 k V/60 A negative cathode power supply, a dummy load and the ECRH control system. The results indicate that the APS can meet the requirements of the ECRH system on J-TEXT.     

基于MCNP的伽玛射线吸收与散射实验仿真平台的开发

介绍一种以MCNP为核心的γ射线吸收与散射的仿真实验平台,在MCNP基础上开发出相应的辅助部件。该仿真软件可仿真93种单质材料及2-3种多元素混合物的吸收实验,模拟吸收厚度为0-100cm,厚度增量为0.001cm。仿真散射实验的介质从Li到Am,实验仿真测量的角度与入射射线方向夹角从-90°到90°,角度增量为1°。     

Design and realization of the J-TEXT tokamak central control system

The Joint Texas Experimental Tokamak (J-TEXT), a medium-sized conventional tokamak, serves as a user experimental facility in the China-USA fusion research community. Development of a flexible and easy-to-use J-TEXT central control system (CCS) is of supreme importance for users to coordinate the experimental scenarios with full integration into the discharge operation. This paper describes in detail the structure and functions of the J-TEXT CCS system as well as the performance in practical implementation. Results obtained from both commissioning and routine operations show that the J-TEXT CCS system can offer a satisfactory and effective control that is reliable and stable. The J-TEXT tokamak achieved high-quality performance in its first-ever experimental campaign with this CCS system.     

Development of ITER divertor Thomson scattering support structure design on the basis of engineering analyses

The support structure for divertor Thomson scattering equipment – the front diagnostic rack, which actually plays plugging role of the divertor port, should be designed to sustain the severe ITER conditions. Meeting the requirements of multifield analyses (which often contradict each other) results in an iterative design process. A number of design variants based on engineering analyses results were developed in 2011–2012. We study here the close to the final design of the diagnostic rack for consistency to electromagnetic, thermal and seismic loads. The specific ITER environment imposes a restricted list of materials and requires a careful design of optical elements to accommodate their thermal expansion. Special attention is focused on the mirror deformed shape under operating loading conditions and its effect on optical system performance, which is vital for all optical systems with mirrors specially designed for the ITER.     

The upgrade of the J-TEXT experimental data access and management system

The experimental data of J-TEXT tokamak are stored in the MDSplus database. The old J-TEXT data access system is based on the tools provided by MDSplus. Since the number of signals is huge, the data retrieval for an experiment is difficult. To solve this problem, the J-TEXT experimental data access and management system (DAMS) based on MDSplus has been developed. The DAMS left the old MDSplus system unchanged providing new tools, which can help users to handle all signals as well as to retrieve signals they need thanks to the user information requirements. The DAMS also offers users a way to create their jScope configuration files which can be downloaded to the local computer. In addition, the DAMS provides a JWeb-Scope tool to visualize the signal in a browser. JWeb-Scope adopts segment strategy to read massive data efficiently. Users can plot one or more signals on their own choice and zoom-in, zoom-out smoothly. The whole system is based on B/S model, so that the users only need of the browsers to access the DAMS. The DAMS has been tested and it has a better user experience. It will be integrated into the J-TEXT remote participation system later.     

Recent progress of the ECRH system and initial experimental results on the J-TEXT tokamak

In order to broaden the range of the plasma parameters and provide experimental conditions for physical research into high-performance plasma, the development of the electron cyclotron resonance heating (ECRH) system for the J-TEXT tokamak was initiated in 2017. For the first stage, the ECRH system operated successfully with one 105 GHz/500 kW/1 s gyrotron in 2019. More than 400 kW electron cyclotron (EC) wave power has been injected into the plasma successfully, raising the core electron temperature to 1.5 keV. In 2022, another 105 GHz/500 kW/1 s gyrotron completed commissioning tests which signifies that the ECRH system could generate an EC wave power of 1 MW in total. Under the support of the ECRH system, various physical experiments have been carried out on J-TEXT. The electron thermal transport in ECRH plasmas has been investigated. When ECRH is turned on, the electron thermal diffusivity significantly increases. The runaway current is elevated when a disruption occurs during ECRH heating. When the injected EC wave power is 400 kW, the conversion efficiency of runaway current increases from 35% to 75%. Fast electron behavior is observed in electron cyclotron current drive (ECCD) plasma by the fast electron bremsstrahlung diagnostic (FEB). The increase in the FEB intensity implies that ECCD could generate fast electrons. A successful startup with a 200 kW ECW is achieved. With the upgrade of the ECRH system, the J-TEXT operational range could be expanded and further relevant research could be conducted.